1. Field of the Invention
This invention relates to an ink jet -recording apparatus for recording an image by transforming a liquid ink to droplets and injecting them onto a recording medium, and more particularly to an ink jet recording apparatus for recording an image on a recording medium by injecting ink droplets by the pressure of supersonic beams irradiated from a piezoelectric element.
2. Description of the Related Art
An apparatus for recording an image by transforming a liquid ink to small droplets and injecting them onto a recording medium has been used practically as an ink jet printer. Although various ink jet printers were invented up to now, a type in which ink droplets are injected by a pressure of vapor generated by heat of a heating body, disclosed in Japanese Patent Publication (Kokoku) No.56-9429 and No. 61-59911 and a type in which ink droplets are injected by pressure pulses mechanically generated by a piezoelectric body, disclosed in Japanese Patent Publication (Kokoku) No. 53-12138 are typical methods known up to now.
However, because in the ink jet printers of these types, an ink is injected from an end of a nozzle, an ink liquid is likely to be locally condensed due to vaporization of a solvent in the ink, thereby leading to clogging of individual fine nozzles corresponding to each resolution.
To overcome these disadvantages, supersonic wave methods in which, an ink is injected from the ink surface by a pressure of supersonic wave beams generated from an piezoelectric element, have been proposed in IBM TDB, Vol. 16, No.4, pp.1168 (1973-10), Japanese Patent Disclosure No. 63-166548, Japanese Patent Disclosure No.63-312157, Japanese Patent Disclosure No. 2-184443 and the like. Because this supersonic wave method is a nozzleless type which does not require individual nozzles for each dot size and partition walls for ink path, this provides an effective structure for preventing the clogging which is a large obstacle for forming of a line head. Further, because this method is capable of generating and injecting very small diameter of ink particles stably, this is suitable for higher resolution type.
In the ink jet recording apparatus using a liquid ink, if it is left not used for a long time, injection of the ink droplets becomes unstable so that deterioration of recorded image quality is induced. According to the related art, to overcome the unstable injection of the ink liquid as described above, a method in which an ink liquid is injected to other area than a recording medium every predetermined time so as to introduce the ink liquid to initial state and a method in which an ink in the nozzle is forcibly sucked into the outside of ink holding means by a pump or the like have been utilized. However, in these cases, the apparatus becomes complicated.